<!doctype html>
<html>
<style>
div::first-line {
  --bar: left;
}
span {
  animation: var(--bar) 5s infinite alternate;
}
@keyframes left {
  from {left: 0;}
  to {left: 30px;}
}
</style>
<div>
  <span>Crash</span>
</div>
</html>
